docs: give a working Docker example

README.markdown

@@ -75,7 +75,7 @@ See the [installation instructions](https://tinygo.readthedocs.io/en/latest/inst
 A docker container exists for easy access to the `tinygo` CLI:
 
 ```sh
-$ docker run --rm -v $(pwd):/src tinygo/tinygo build -o /src/blinky.elf -target arduino /src/examples/blinky
+$ docker run --rm -v $(pwd):/src tinygo/tinygo build -o /src/wasm.wasm -target wasm examples/wasm
 ```
 
 Note that you cannot run `tinygo flash` from inside the docker container,

docs/docker.rst

@@ -5,10 +5,11 @@
 Using with Docker
 =================
 
-A docker container exists for easy access to the ``tinygo`` CLI.
-For example, to compile the blinky example from the root of the repository::
+A docker container exists for easy access to the ``tinygo`` CLI. For example, to
+compile ``wasm.wasm`` for the WebAssembly example, from the root of the
+repository::
 
-    docker run --rm -v $(pwd):/src tinygo/tinygo build -o /src/blinky.elf -target arduino /src/examples/blinky
+    docker run --rm -v $(pwd):/src tinygo/tinygo build -o /src/wasm.wasm -target wasm examples/wasm
 
 Note that you cannot run ``tinygo flash`` from inside the docker container,
 so it is less useful for microcontroller development.